1. Field of the Invention
The present invention relates generally to an examining apparatus for examining a visual recognition apparatus and, more particularly, to a dot pattern-examining apparatus for examining whether or not the visual recognition apparatus correctly displays a dot pattern on a display screen by means of liquid crystal, light emitting diodes or the like.
2. Description of Related Art
In order to examine the display function of the visual recognition apparatus which displays a dot pattern by means of the liquid crystal or the light emitting diodes, the dot pattern-examining apparatus picks up and processes the dot pattern formed by the luminescence of the liquid crystal or the light emitting diodes and compares a two-dimensional image of the dot pattern formed on a display screen with a reference dot pattern. In this manner, the dot pattern-examining apparatus examines whether or not the liquid crystal or the light emitting diodes have formed a correct dot pattern.
A conventional dot pattern-examining apparatus is described below with reference to FIGS. 9A and 9B. FIG. 9A depicts a partial image template having a reference dot pattern formed thereon, while FIG. 9B depicts a two-dimensional image of the display screen on which a target dot pattern is displayed.
In order to examine the target dot pattern from among various dot patterns contained in the two-dimensional image by means of image processing, it is necessary for the dot pattern-examining apparatus to find the position of the target dot pattern.
To this end, the conventional dot pattern-examining apparatus first scans the two-dimensional image of the display screen and subsequently compares each of the various dot patterns contained in the two-dimensional image with the reference dot pattern of the partial image template of FIG. 9A. Then, the dot pattern-examining apparatus determines an area having a dot pattern which most matches the reference dot pattern as the area having the target dot pattern.
The conventional dot pattern-examining apparatus generally uses either hardware or software to find the area having the most matching dot pattern. In either case, each of the dot patterns formed on the display screen is directly compared with the reference dot pattern of the partial image template. It is, therefore, necessary to compare dots of the former with those of the latter one by one to determine the degree of matching and, hence, the processing requires much time.
In the method of using the hardware, the use of a large partial image template for high-accuracy examination enlarges the size of the hardware. Thus, this method costs high. The method of using the software requires much processing time and is, hence, impractical. In addition, because partial image data themselves are used as a template, the memory capacity therefor increases.
In some cases, various reference dot patterns are required to examine the corresponding dot patterns contained in the two-dimensional image of the display screen. In this case, if some of the dot patterns to be examined are inclined, it is necessary to additionally prepare a plurality of reference dot patterns having different inclinations for each reference dot pattern. Nevertheless, it is difficult for the conventional dot pattern-examining apparatus to detect such an angular deviation accurately.
Further, if a binary image is used in pattern matching, the apparatus is incapable of making a correct examination in the presence of nonuniformity in illumination. In order to overcome this problem, there is a method of first preparing a background image having illumination nonuniformity and subsequently converting a dot pattern into binary form by calculating the difference in density between the dot pattern and the background image. This method is, however, incapable of coping with illumination nonuniformity which changes with time. In addition, the use of a gray image requires much processing time for pattern matching and, hence, this method is impractical.